1. Field of the Invention
This invention relates generally to providing discrete stiffeners to reinforce a panel and, more particularly, to securing thermoplastic injection molded discrete stiffeners to a back surface of a show surface panel of an automotive trim panel.
2. Discussion of the Related Art
Trim panels on a vehicle, such as fascias, rockers, door moldings, etc., typically have an outward facing show surface, sometimes referred to as a class-A surface, that gives the panel an aesthetically pleasing appearance. Providing such show surfaces often requires relatively expensive materials and manufacturing processes. Thus, trim panels are typically made very thin to conserve cost. However, such trim panels often times have a two-dimensional or three-dimensional curvature and are required to be stiff enough to resist various loads without excessive deformation. In response to this, it is known in the art to make a trim panel as a two-piece structure including an outer show surface panel and an internal support structure often including a series of stiffening ribs forming a frame that provides structural integrity. The support structure may include a series of welding pads integrated into the support structure at locations where the ribs intersect. The welding pads have the general shape of the show surface panel and are used to ultrasonically weld the support structure to an inside surface of the show surface panel. The stiffness of the trim panel is set mainly by the height, thickness and spacing of the ribs.
In order to reduce cost and weight, it is desirable to limit the number of ribs in the support structure, which also reduces its stiffening capability. Thus, the ribs are generally selectively positioned and provided with different heights depending on where the structural integrity of the particular trim panel is desired. However, the height of the ribs is limited by the packaging volume of the trim panel. Further, although the show surface panel does possess some inherent stiffness, most of the stiffness is provided by the rib structure. Therefore, in order to further reduce the cost of the trim panel, it is desirable to make the show surface panel as thin as possible consistent with the ability of the support structure to provide the desired rigidity. However, because the support structure is welded to the show surface panel, there are limits as to how thin the show surface panel can be because the welding operation could cause imperfections on the show surface of the show surface panel if it is too thin. Further, for some types of trim panels, the panel is required to have a high degree of curvature to be formed at a desirable location. For these types of panels, traditional stiffeners, such as rib stiffeners, have not been adequate to provide local stiffening at high curvature areas.